If You Give a Cat a Cupcake by Laura Numeroff is an easy book to come up with additional activities for. We had so much fun with it!
This book fit really well into our “C” theme week. After reading If You Give a Cat a Cupcake, the kids helped me make cupcakes.
Later, they each took a turn decorating one for themselves and one to send home with my friend Glenda for her kids.
I set out three colours of icing, a tube of orange icing for ease of decorating, sprinkles, and small candies. The kids loved the freedom of decorating their own cupcake in any way they wanted. 
Almost as much fun as decorating (and eating!) the cupcakes was decorating paper ones using a printout I found here.
I provided glue, candy sprinkles (leftover from decorating the edible cupcakes), sequins, and coloured markers. I love how creative they were with their pictures, especially how they coloured their cupcake wrappers. 
The kids also did a character match-up based on the book and this ‘C is for Cupcake’ sheet from Spell Out Loud.
Finally, we set about creating our own poems based on the format of If You Give a Cat a Cupcake. If you give a _________ a ____________, he will _____________.
More If You Give a Cat a Cupcake Activities:
Cupcake Match Cards from No Time for Flash Cards
If You Give a Cat a Cupcake Cupcake Craft from I Heart Crafty Things
Cupcake Ornaments from Happiness is Homemade
Foam Dough Cupcake Making Station from I Heart Crafty Things (so cute and it has a sensory element too which I love!)
Laura Nemeroff Inspired Writing Activities over at Trinity Preschool (such great ideas for many of her books including If You Give a Cat a Cupcake)
You may also be interested in these other book activities:
The Very Hungry Caterpillar Activities 
A Bad Case of Stripes Activities 
Fancy Nancy Activities 